This application claims the priority benefit of Taiwan application serial no. 89118676, filed Sep. 13, 2000.
1. Field of the Invention
The present invention relates to a method of repairing and cleaning a half-tone phase shifting mask (HTPSM). More particularly, the present invention relates to a method, wherein an etching is employed and the etching is applicable for etching a quartz substrate according to the thickness consumption of the MoSiON phase shifter layer, which then allows the phase difference of a mask to remain relatively unchanged after washing or repeated repairing.
2. Description of the Related Art
In the current photolithography procedure, a phase shifting mask can be used to raise the resolution of pattern transfer during a photolithographic procedure. Usually, an ultraviolet light is used as the light source when the stepper is implementing an exposure process. Consequently, the ultimate resolution provided by the exposure system hinges on the wavelength of the light source that is being used. The important parameters that defines the exposure system""s pattern-transfer ability include the parameter of the lowest resolution provided by the exposure system and the depth of focus (DOF) of exposure system. The lower is the lowest resolution, the higher is the DOF, and the better the exposure effect. However, the wavelength of the light source has an opposite effect on these two parameters. In another words, when the wavelength of the light source is short, even if the exposure system can provide a relatively low resolution, the DOF is reduced at the same time. Thus, when designing an exposure system, one must consider the pros and the cons of resolution and the tradeoffs in the DOF.
In the conventional phase shifting photolithography a few phase shifter layers added to the original traditional mask are used. Through the positive and negative interference derived from these phase shifter layers during an exposure, the image pattern projected on the chip has a better resolution. A special feature of the conventional phase shifting lithography is that it does not require the use of a new light source. Merely performing the repairs on the mask, the resolution ability of the exposure system is increased to its original status. However, in the existing technique for a mask manufacturing, multiple repairs cannot be done. Since every repair causes the thickness of the phase shifter layer to thin out and the phase difference between mask substrate to change, the mask cannot be used after the repair.
FIGS. 1A to 1E are schematic diagrams in cross-sectional view illustrating a PSM manufacturing method in the prior art.
Referring to FIG. 1A, a construction of a mask substrate 100 is provided, wherein the substrate can be made of a material such as quartz with relatively good translucency. Next, on the substrate 100 are sequentially formed a phase shifter layer 102, an opaque shield layer 104 and a photoresist layer 106. The phase shifter layer 102 is made of a material such as MoSiON, the opaque shield layer 104 is made of a thin film of chrome or a chrome oxide.
Subsequently, referring to FIG. 1B, the photolithographic procedure is used to define the photoresist layer 106, and dry etching is used to etch the opaque shield layer 104, thereby exposing the phase shifter layer 102.
Referring to FIG. 1C, the phase shifter layer 102 is etched, thereby exposing a portion of the substrate 100.
Furthermore, referring to FIG. 1D, the photoresist layer 106 is removed and another photoresist 108 layer is coated, and using the photoresist layer 108 as a mask, another portion of the opaque shield layer 104 is removed.
Finally, referring to FIG. 1E, the photoresist layer 108 of ID is removed. The above-described removal of the photoresist layers 106 and 108 is usually performed by using a sulfuric acid/hydrogen peroxide (H2SO4/H2O2) solution. However, this procedure usually would result with a part of the photoresist layer and defective particles remaining, influencing the quality of the PSM. When there is too much defective particle residue or if the opaque shield is defective, repairs and cleaning must be performed on the mask. Consequently, the prior art still uses a SC1 (NH3/H2O2/H2O solution to perform deep cleaning in order to remove the excess defective particles on the PSM.
In the PSM reworked cleaning process of the prior art in which the SC1 solution is used for the cleaning, the SC1 solution also etches the phase shifter and reduces the thickness of the phase shifter, causing the phase difference between the substrate and the phase shifter to change. If the phase difference is too large, then the mask cannot be used. If SC1 solution is not used, then removing the defective particles becomes a difficult task.
In view of the above, the present invention provides a method to enable the PSM to be cleaned or to have repeated repairs without generating the disadvantageous phase difference as in the prior art.
As embodied and broadly described herein, the invention provides a PSM manufacturing method, at least including providing a substrate and forming sequentially a phase shifter layer and an opaque shield layer on the substrate. The phase shifter layer and the opaque shield layer are then defined. An etching is further conducted on the substrate to a predetermined depth, exposing a portion of the substrate. A cleaning procedure is performed, wherein the cleaning procedure etches a portion of the phase shifter surface, and the predetermined depth is decided based on how much of the phase shifter is etched during the cleaning procedure.
According to a preferred embodiment of the invention, the substrate material is quartz, the phase shifter material is MoSiON and the opaque shield material is chrome or chrome oxide. Compensated by the etching procedure, the phase difference between the substrate and the phase shifter layer after the definition of the opaque shield layer and the phase shifter layer is the same as the phase difference between the substrate and the phase shifter layer after the cleaning process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.